1. Field of the Invention
The present invention relates to a modular jack in a modular connector adopted to be provided for an electronic appliance such as a telephone, a facsimile or the like.
2. Description of Prior Art
As measures to suppress noise of an electronic appliance in which an modular jack is employed, the followings have been known: (1) providing a pair of three-terminal capacitors 6 on a circuit board 4 such as a printed board on which a modular jack 2 is mounted (see FIG. 11), and (2) providing a common mode choke coil 8 on the circuit board 4 on which the modular jack 2 is mounted (see FIG. 12).
Each of the three-terminal capacitors 6 has an equivalent circuit as shown in FIG. 13, and noise is brought outside through an earth. The common mode choke coil 8 has an equivalent circuit as shown in FIG. 14, and two coils coiled on a core in the opposite direction eliminates common mode noise. However, using an additional part like the pair of three-terminal capacitors 6 or the common mode choke coil 8 consumes space on the circuit board 4 (such an additional part sometimes requires more space than the modular jack 2), which interferes with making the electronic appliance compact. Further, in both ways, since the pair of capacitors 6 or the common mode choke coil 8 is away from the modular jack 2, the appliance receives external noise.
In the light of these problems, we disclosed in U.S. Pat. No. 5,015,204 and German patent DE-AS-202342 a modular jack containing a common mode choke coil which comprises a ring-shaped core and two coils coiled thereon. One end of the coils is made to be a contactor with a plug, and the other end is made to be a terminal to be used for mounting the modular jack on a circuit board. The modular jack according to the invention has advantages that it functions as a noise suppressor because it contains a common mode choke coil and that it is compact because a coil, a contactor and a terminal are made into a unit. However, the modular jack has the following drawbacks. In plating the contactor and the terminal, the coil will be plated unnecessarily because the coil, the contactor and the terminal are made into a unit, and this increases production cost. In order to increase the number of signal circuits, more common mode choke coils are necessary, which requires more space for cores, and the modular jack cannot be made compact. Because of the cores, the pitch among the terminals is more than the pitch 1.02 mm of an ordinary circuit board on which the modular jack is mounted, and a newly designed circuit board will be required.